This invention relates to wet process chemistry treatment of substrates, e.g., semiconductor wafers and the like, and is more particularly directed to a technique for planing or etching the surface of a flat workpiece so that it is left uniformly flat across the surface. The invention also concerns a technique that facilitates employment of robotic handling of the articles to be planed e.g. between plating steps.
Electroplating plays a significant role in the production of many rather sophisticated technology products, such as masters and stampers for use in producing digital compact discs or in the manufacturing of advanced semiconductor wafers. However, as these products have become more and more sophisticated, the tolerances of the plating process have become narrower and narrower. Current plans to increase the circuit density of silicon wafers are being thwarted by the inability of plating techniques to control unevenness in the plating process, and especially in the axial direction.
It is the current practice to employ an electrolytic etch technique to remove a surface layer from a wafer, for example after a plating step. In this technique, the wafer is held vertically, i.e, in a vertical or nearly vertical plane, and is sprayed or injected with an etchant electrolytic solution. There can be a cathode for applying an electric current across the solution to the surface of the wafer. The electrolyte then runs down the front of the wafer and drips off from the bottom edge. This creates a conductivity path through the electrolyte back to the cathode. Thus in this arrangement, even if the electrolyte does remove the material evenly at the point where the electrolyte is sprayed on, metallization can be uneven below that point. The planing is less than optimal. Also, any particles that may become entrained in the electrolyte continue down the face of the wafer and can deposit on other parts of the wafer. While it would be an improvement to hold the wafer horizontally and spray the electrolyte onto the horizontal wafer, it has not been possible to spray the electrolyte onto a horizontal surface and then collect it again. Thus a technique to produce a truly flat electro-planed workpiece has eluded the industry.